Bell Communications Research (Bellcore) and BellSouth Telecommunications have established more stringent requirements for electronic equipment cabinets. These customized cabinets are intended to house various types of telecommunications equipment, including active electronic and optical systems and passive mechanical cross-connect and splicing fields. The cabinets are required to protect the electronics equipment from a wide range of ambient temperatures and inclement climatic conditions including rain, snow, sleet, high winds, wind driven rain, ice, and sand storms. These cabinets must pass stringent weathertightness rain intrusion, wind driven rain intrusion, salt fog spray, temperature cycling, and high humidity tests. Bellcore's General Requirements for Electronic Equipment Cabinets, Technical Advisory TA-NWT-000487, Issue 2, June 1993, and BellSouth Telecommunications' Electronic Equipment Cabinets (Subscriber Carrier/Fiber in the Loop), Specification BS-631-0032, Issue 1, November 1992, may be consulted for a detailed description of the requirements and the test criteria. To provide weathertightness, all possible entry points for moisture must be either welded closed or sealed.
In addition to the weathertightness requirement is the need to cool the heated air internal to the cabinet enclosure. The electronics equipment housed by the cabinets generate large amounts of heat that must be dissipated to avoid equipment failure. The cooling system must provide entry and exit points for external ambient air to remove heat gain accumulated in the cabinet. However, the external air entry and exit points must be well-guarded against driving rain and other intrusive moisture. Further, the cooling system is required to circulate air within the cabinet efficiently and evenly without leaving pockets of hot air. Prior equipment cabinets require the use of distributed fans or fan trays located at various spots in the cabinet to circulate air. This is not cost-effective and takes up additional room in the cabinet.